But..
"if PrivacyShield is deemed adequate for transfers of personal data from the European Union(EU) to the USA"
But it isn't. The only thing that would be adequate is wholesale change of US constitutional law to cover non-US citizens outside the US; which is never going to happen in - even with legislative branch support (which there is none: they think it's hilarious that people outside the US have expectations of a right to privacy. No really, they actually laughed when they were asked about it) - more than 25 years, best case really.
People hiding behind this stuff are ignoring the basics of the issue that brought Safe Harbour crashing down. That the 4th amendment doesn't cover non-US citizens outside the US and that the president has the power to do pretty much whatever he/she(? maybe?) wants even if it did. Corps in the US have zero control over any of this and are in no position to certify, guarantee, prove, attest, swear by anything.
As Caspar Bowden said, the only thing they're really going to understand is stopping the data flows.
I don't think it's even fit for the UK either if we get the kind of law that's been floated recently, there's effectively zero checks and balances in there so..